1. Field of the Invention
The present invention relates to imaging systems and more particularly to positioning of wafer lenses on imager dies.
2. Description of Related Art
Electronic imagers are commonly used in photo-imaging applications. The imager is typically formed from charge-coupled-devices (CCD) or complementary metal oxide semiconductor (CMOS) devices. The imager contain many thousands of transistors which define pixels arranged in an array. The pixels are used to convert light into electrical signals that can then be stored and recalled by a processing device to produce an image.
Imagers can be formed in various structures. For example, they can be formed as separate imager dies, as part of chip scale packaging (CSP), or as part of through-silicon via (TSV) modules. Regardless of the particular construction, however, a lens is generally required to focus an image upon the pixels of an imager die. The lens must be positioned at a precise focal distance from the surface of the imager die in order to produce a sharp image. In the case of imagers used in devices such as mobile phones, the lens is typically set to a fixed focal position.
As the demand for smaller imaging devices has increased, optical tolerances become smaller, thereby increasing the level of precision required for positioning the lens relative to the imager. In many devices, the lens system is constructed directly on the imager, which means a method of attaching the lens to the imager is required. Conventional fabrication techniques use a lens barrel or a fixed stand-off to achieve the required focal length. However, conventional lens barrels or lens stand-off s can increase cost, and are not easily adjusted to achieve optimal image quality. For example, these techniques do not allow compensation for a wide range of tolerance issues within the lens, imager and any additional cover glass associated with the imaging device.